Theravada Buddhism, most closely linked to Siddhartha Gautama's historical teachings is essentially a moral philosophy (with broad-stroke metaphysical and epistemological teachings reinforced entirely by contemporary naturalistic academia). As buddhist teachings spread into Eastern Asia, and what we call 'zen' teachings developed originally in China, and into the Himalayan region (commonly known today as Vajrayana, and taken together with the East Asian tradition, referred to collectively as Mahayana) the teachings amalgamated localised (and more traditionally 'religious') folk beliefs. Incidentally, these should be considered seperate from the core Buddhist teachings, which continue to emphasise a lack of human 'soul', the transience of all things in nature, karma in a psychological context and divorced of superstitious connotations, the importance of 'reason' above all other human faculties, and a rejection of authority in either scripture or personality (other key concepts in all religions, supernatural and otherwise).
One of the things that you have to do to become a Buddhist is to take refuge in the Three Jewels: the Buddha, the Dhamma, the Sangha.
The Buddha is absolutely authoritative in Buddhism. He is someone you trust, someone you believe in, someone you have faith in. Why? Because he had direct experience. He tasted nibbana. He was once a man, but now is something more than gods and men. He is the Awakened One. Like other religions, the Buddha desired people to test their beliefs so far as possible.
Through testing, one's faith in the Buddha, his Dharma and the Sangha grows stronger and stronger. There are other beliefs that are untestable (as of yet), such as the perfect reclamation of one's part rebirths. Here, you must simply trust the Buddha to know, until the moment when one can progress to the point where one can also directly apprehend the memories of one's past lives. How can you believe that nirvana is attainable, unless you trust the Buddha's words? For a good read of how faith is important to Buddhism, read:
saddhā and also
here.
Stripping Buddhism of the supernatural is as silly as stripping Jesus from Christianity. Let me just take one example.
In the Noble Eightfold Path, there is the precept Right View. You must have Right View and not wrong view. One of the Wrong Views was ucchedavāda, which can be pretty much described as materialism. In the Buddha's time, there were eternalists, people who believed in the existence of a soul. And there were the annihilationists, who believed in the doctrine of annihilationism. They believed that when they died, they would be annihilated, no afterlife and no nothing.
The Buddha firmly rejects both extremes and teaches the Middle Way.
If there is no rebirth, there's no nirvana. And the Buddhist path becomes...well, pointless. The cessation of suffering is indefatigably linked with rebirth by the Buddha. You can scarcely read five pages of the Pali Canon without hearing about it. Here's just one, the
Itivuttaka 49:
This was said by the Lord...
"Bhikkhus, held by two kinds of views, some devas and
human beings hold back and some overreach; only those with vision see.
"And how, bhikkhus, do some hold back? Devas and humans enjoy being, delight in being, are satisfied with being. When Dhamma is taught to them for the cessation of being, their minds do not enter into it or acquire confidence in it or settle upon it or become resolved upon it. Thus, bhikkhus, do some hold back.
"How, bhikkhus, do some overreach? Now some are troubled, ashamed, and disgusted by this very same being and they rejoice in (the idea of) non-being, asserting: 'In as much as this self, good sirs, when the body perishes at death, is annihilated and destroyed and does not exist after death — this is peaceful, this is excellent, this is reality!' Thus, bhikkhus, do some overreach.
"How, bhikkhus, do those with vision see? Herein a bhikkhu sees what has come to be as having come to be. Having seen it thus, he practices the course for turning away, for dispassion, for the cessation of what has come to be. Thus, bhikkhus, do those with vision see."
Having seen what has come to be As having come to be, Passing beyond what has come to be, They are released in accordance with truth By exhausting the craving for being. When a bhikkhu has fully understood That which has come to be as such, Free from craving to be this or that, By the extinction of what has come to be He comes no more to renewal of being.
This too is the meaning of what was said by the Lord, so I heard.
Devas are gods. The Buddha talks to the gods in the scriptures. These are from the Pali Canon mind you.
One of my favourite teachings of the Buddha is the
Assu Sutta:
At Savatthi. There the Blessed One said: "From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. What do you think, monks: Which is greater, the tears you have shed while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — or the water in the four great oceans?"
"As we understand the Dhamma taught to us by the Blessed One, this is the greater: the tears we have shed while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — not the water in the four great oceans."
"Excellent, monks. Excellent. It is excellent that you thus understand the Dhamma taught by me.
"This is the greater: the tears you have shed while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — not the water in the four great oceans.
"Long have you (repeatedly) experienced the death of a mother. The tears you have shed over the death of a mother while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — are greater than the water in the four great oceans.
"Long have you (repeatedly) experienced the death of a father... the death of a brother... the death of a sister... the death of a son... the death of a daughter... loss with regard to relatives... loss with regard to wealth... loss with regard to disease. The tears you have shed over loss with regard to disease while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — are greater than the water in the four great oceans.
"Why is that? From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries — enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released."
We must leave this interminable wandering through existence, being reborn over and over and over and over and over and over.
All the above is standard Theravada practice and belief. I personally find myself more attracted to Mahayana.
Regarding meditative practice, these practices may (and should) be considered completely seperate from any sort of supernatural ideas (they are, with the exception of Vajrayana tantric practices, the complete opposite). Likewise, the Buddha's ethical teachings were entirely secular and are void of appeal to any sort of authority or moral objectivity (taking India's existing metaphysical and physical understanding as a starting point, the historical Buddha's additions to/rejections of the commonly accepted models of the day were entirely secular; contrast this to the supernatural fulfillment of existing illiterate prophesy that was Hebrew understanding of the world order in the time of Jesus).
Buddhism is one of my favourite religions. I don't recognise your depiction of Buddhism here. There are a great many Buddhists on this board that could correct your understanding of the history of Buddhism.
I find it strange how your understanding of Buddhism so closely matches your own beliefs about how the world is. Again, I have to ask: what are your motives, your intentions, your reasons behind the views that you hold?